Assessment of Periodical Ice Loads Acting on Screw Propeller During its Interaction with Ice

Abstract

Periodical ice loads on blades of the screw propeller of icebreakers and ice-going ships are one of the reasons for occurrence of fatigue damages of the propulsion system structures as well as for generation of the ship hull vibration. The paper describes an approach of the Krylov Shipbuilding Research Institute, St. Petersburg, to the problem of determination the oscillation of propeller thrust and torque during interaction with ice, and spectra of these loads. A comprehensive approach to this problem includes three lines of investigations, namely, an application of a theoretical model and two types of model tests that are to be performed in the Ice Basin: tests of ice milling by screw propeller model with use of a free-water unit and towing testing of a ship model with working propulsion devices. Each of the investigations lines has its limited capacity and, at the same time, supplements general picture of the complicated process under consideration. The estimated values of periodical ice loads on the propeller may be applied to fatigue strength analysis of structures of the propulsion system or to numerical estimation of vibration characteristics of ice going ship. An example of such calculation of vibration characteristics is shown in the paper. It has indicated that the general ship hull vibration in specified ice conditions can be 3-4 times greater, if ice induced periodical loads on the propellers are taken into account. Periodical ice loads on blades of the screw propeller of icebreakers and ice-going ships are one of the reasons for occurrence of fatigue damages of the propulsion system structures as well as for generation of the ship hull vibration. The paper describes an approach of the Krylov Shipbuilding Research Institute, St. Petersburg, to the problem of determination the oscillation of propeller thrust and torque during interaction with ice, and spectra of these loads. A comprehensive approach to this problem includes three lines of investigations, namely, an application of a theoretical model and two types of model tests that are to be performed in the Ice Basin: tests of ice milling by screw propeller model with use of a free-water unit and towing testing of a ship model with working propulsion devices. Each of the investigations lines has its limited capacity and, at the same time, supplements general picture of the complicated process under consideration. The estimated values of periodical ice loads on the propeller may be applied to fatigue strength analysis of structures of the propulsion system or to numerical estimation of vibration characteristics of icegoing ship. An example of such calculation of vibration characteristics is shown in the paper. It has indicated that the general ship hull vibration in specified ice conditions can be 3-4 times greater, if ice induced periodical loads on the propellers are taken into account.